Efforts to reform the health care system have centered on the goal of reducing the high rate of uninsurance. One proposal that has received considerable discussion, but scant empirical analysis, is a prohibition on underwriting, the process by which health insurers choose whom they will insure. The proposal is supported by ethicists who contend that underwriting is morally indefensible and market reformers who view underwriting as a barrier to insurance for those in poor health. Health insurers oppose restrictions on underwriting. Despite the current national prominence of the debate on underwriting, the issue is not a new one. Each of the states has passed regulations that restrict the ability of health insurers to use particular types of information for underwriting purposes, including denying coverage and charging differential premiums. Determination of the effect of the underwriting restrictions imposed in the different states on the rate of uninsurance is the central focus of the proposed research project. In theory underwriting restrictions will decrease the price of insurance charged to those who would have been classified as high risks were underwriting permitted. Consequently a higher rate of purchase by this group is expected. Conversely, underwriting restrictions are expected to result in a higher price and lower rate of purchase for those who would have been classified as low risks had underwriting been permitted. The effect of prohibitions on the use of gender, marital status, age ,race and degree of physical impairment as underwriting criteria will be studied. The impact t of these restrictions on different subpopulations and on the population as a whole will be tested. A prior underwriting restriction may increase or decrease the overall level of uninsurance in a state. The proposed study employs a multinomial model and panel data methods to analyze health insurance coverage data reported in the current population survey. Information on underwriting restrictions will be compiled from state statutes. The knowledge to be gained from this study has direct implications for public policy focused on health insurance reform. If underwriting restrictions are associated with reductions in the rate of uninsurance, this type of market reform holds promise as a way to address in part the problem of uninsurance in the country. If, on the other hand, the restrictions result in a greater degree of uninsurance, they are ill advised.